Generally, in a CMOS (complementary metal oxide semiconductor) sensor, a plurality of pixels having photodiodes are arranged in a matrix pattern, and pixel signals corresponding to charges generated through photoelectric conversion performed by the photodiodes are output from the respective pixels.
Also, the respective pixels of the CMOS sensor have transistors for controlling the output of pixel signals, and pixel signals are output in units of lines (rows) or in units of pixels in response to control signals that specify addresses of rows and columns.
For example, each pixel is configured including four transistors: a transfer transistor; a reset transistor; an amplifying transistor; and a selection transistor. Also, a node connecting the transfer transistor, the reset transistor, and the amplifying transistor constitutes a floating diffusion that accumulates a charge generated through photoelectric conversion performed by the photodiode and that converts the charge into a voltage.
The transfer transistor transfers the charge generated through photoelectric conversion performed by the photodiode to the floating diffusion. The reset transistor resets the charge accumulated in the floating diffusion. The amplifying transistor amplifies the voltage according to the charge accumulated in the floating diffusion. The selection transistor outputs the voltage amplified by the amplifying transistor, that is, a pixel signal, to a vertical signal line.
That is, in the CMOS sensor, the respective transistors are controlled, whereby a process of transferring a charge accumulated in the photodiode to the floating diffusion and a process of outputting a pixel signal are performed in units of rows or in units of pixels. Also, in the CMOS sensor, a process of resetting the charge previously accumulated in a photodiode at the start of exposure of a pixel and resetting the charge accumulated in a photodiode and a floating diffusion due to exposure at the end of exposure of a pixel (hereinafter called rolling shutter as necessary) is performed.
Also, in the CMOS sensor, a process of cropping the angle of view or a thinning process is performed to capture an image in which the number of pixels is smaller than the total number of pixels. For example, in a thinning process, the pixels from which pixel signals are read are thinned down at the intervals of several rows and several columns, so that an image is captured using pixel signals read from some of the pixels.
In such a thinning process or the like, there are pixels from which pixel signals are not read, and a rolling shutter for controlling the starting and ending of accumulation of a charge is not applied to those non-read pixels, which are pixels from which pixel signals are not read, so that a blooming phenomenon occurs. The blooming phenomenon is a phenomenon in which, when a charge is generated through photoelectric conversion beyond the maximum amount of charge the photodiode can accumulate, the charge overflows (leaks) from the photodiode and passes through a transfer transistor and a channel-stop region, so as to flow into a floating diffusion or another adjoining pixel.
When the blooming phenomenon occurs, a white zonal or white circular pattern appears in an image, which may degrade image quality.
As measures against the blooming phenomenon, it is applicable to provide, on pixels from which pixel signals are not read, a shutter for resetting a charge accumulated in the photodiode and avoiding the blooming phenomenon.
However, in order to provide a shutter for avoiding the blooming phenomenon, a circuit and an address line dedicated to performing the process need to be added to the CMOS sensor. In order to deal with various imaging modes, a process of cropping the angle of view or a thinning process corresponding to the respective imaging modes needs to be handled, and thus the dedicated circuit for providing a shutter for avoiding the blooming phenomenon becomes complicated and the circuit scale thereof increases.
Furthermore, this dedicated circuit is dedicated to a specific imaging mode, and the circuit needs to be modified or a circuit needs to be newly added when the imaging mode is modified or another imaging mode is added, so that it is difficult to respond to modification or addition of an imaging mode. Also, in a case of preparing a dedicated address line, many address lines are required and a dedicated address decoding circuit is also required. For this reason, in a case where many imaging modes exist, a method for combining address lines for a shutter for avoiding the blooming phenomenon and a dedicated circuit is used. However, the circuit becomes complicated and the circuit scale thereof increases. Also, in an address control device that manages shutter positions, the number of shutter positions required to be managed increases and complexity occurs, and as a result, the circuit scale of the address control device increases.
Also, in pixels from which pixel signals are read, if intense light enters a photodiode before a rolling shutter is applied, a charge overflows from the photodiode and the blooming phenomenon occurs. Also, in a case where an adjoining pixel is being exposed, an unnecessary charge is accumulated in the pixel, which degrades image quality.
Here, there is disclosed a technique of performing time division multiplexing on an address selected by a decoder and selecting a plurality of electronic shutter rows or read rows using one decoder (for example, see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent
Application publication No. 2004-166269